The present invention relates to a semiconductor device having a high resistance to electrostatic and electromagnetic induction, and, more particularly, to an improved shield for a semiconductor device which provides high resistance to electrostatic and electromagnetic induction without reducing the ability of the semiconductor device to withstand adverse environmental conditions.
Semiconductor devices have been used in an ever increasing variety of applications, such as integrated circuits (ICs) and photocouplers. As the fields of application have increased, semiconductor devices have also been subjected to more adverse environmental conditions. As an example, in many applications the air surrounding the semiconductor device is teeming with electromagnetic waves. These waves tend to induce currents in the metallic or conductive portions of the device and cause erroneous and/or faulty operation. Further, in many present day applications semiconductor devices are coupled to circuits wherein large surge voltages, caused by the switching of power circuits, occur in the power line. These voltages, like electromagnetic air waves, tend to induce unwanted currents which result in erroneous operation.
To protect semiconductor devices from operation failure due to such electromagnetic waves and surge voltages, on-chip shield structures have been developed. Such structures generally comprise an insulating film formed over the entire surface of the semiconductor device. For example, Japanese Patent Disclosure No. 60-4257 describes a method for improving IC resistance to electromagnetic radiation by utilizing an on-chip shield. Also, Japanese Patent Disclosure No. 52-79789 describes an on-chip shield for preventing operation failures due to surge voltage induction in a photocoupling semiconductor. However, the above described on-chip shields are subject to failure or temporary operational errors when used in an environment with significant temperature variations. As a result, the device cannot be reliably operated under varying temperature conditions.
It is desirable, therefore, to provide apparatus for shielding a semiconductor device from electromagnetic air waves and power line surge voltages. Further, it is desirable to provide such a device which is also substantially impervious to significant temperature variations. It is also desirable to provide such a device which is particularly suited for use with optical coupling devices. As always, it is desirable to provide such a device while maintaining high yield and simultaneously minimizing production costs.